Upper-crust thermal evolution of the Patagonian Precordillera basement (Argentina): insights from fission track, (U-Th)/He thermochronology and geodynamic significance

The geodynamic evolution of the basement of the Patagonian Precordillera (Argentina) began with middle to late Paleozoic tectonometamorphic and magmatic events. Subsequent exhumation was triggered by brittle-ductile to brittle deformation from Mesozoic to Cenozoic times thought the thermal evolution of this stage is relatively unexplored in most basement areas. In this study, we assess the cooling-thermal evolution in the upper crust, providing new thermal models based on fission-track and (U-Th)/He thermochronology data in zircon and apatite belonging to basement inliers of the Patagonian Precordillera. Most thermal models show similar decreasing time-temperature paths (t-T), from which three stages are distinguished. The Late Triassic – Jurassic stage exhibits a rather undefined cooling trajectory and cooling rates (0.56–2.2°C/My), which are temporally correlated with high magmatic productivity and extensional deformation related to extensional tectonic settings. This first stage might have resulted from coupled tectonothermal processes consisting of extensional faulting and high-temperature gradient. Subsequently, a relatively fast temperature decrease (2.75–5°C/My) for the late Early Cretaceous to Paleocene is likely related to a compressive stage associated with the growth of the early Andean Orogen. Low cooling rates (<1°C/My) characterize the third stage correlative with Palaeogene arc magmatism. Although this low cooling rate remains until present day conditions, one thermal model denotes a final high cooling rate during Miocene linked to the second compression stage of the Andean Orogen. Results thus indicate that one of the most significant exhumation event recorded in basement rocks of the Patagonian Andean foreland took place during the late Early Cretaceous – Paleocene stage.